Selection and Maintenance of Fuel for Diesel Generator Sets

In today's industrial and commercial environment, diesel generator sets are widely used in various scenarios due to their efficiency and reliability, playing an indispensable role from backup power to primary power. However, to ensure the efficient operation and long service life of diesel generator sets, choosing the right fuel is crucial. This article will explore in depth the key indicators of diesel fuel for generator sets, and how to ensure fuel quality through simple testing methods and maintenance measures, thereby safeguarding the performance of the generator set.

The performance and lifespan of diesel generator sets largely depend on the quality of the fuel used. High-quality fuel not only improves the operating efficiency of the generator set but also reduces mechanical wear and the risk of failure. Therefore, it is essential to understand and master the key indicators of diesel fuel for generator sets. Below is a detailed interpretation of several major indicators.

The core power of diesel generator sets comes from the combustion of diesel, and the ignitability of diesel is one of the key factors determining its combustion efficiency. The cetane number is an important indicator for measuring diesel's ignition performance. The higher the cetane number, the lower the auto-ignition temperature of diesel, meaning the diesel is easier to ignite in the engine cylinder, and the ignition delay (the time from the start of injection to ignition) is shorter. A short ignition delay results in fewer combustible gases formed in the cylinder, making combustion gentler and engine operation smoother.

However, a cetane number is not the higher the better. Excessively high cetane values cause heavier distillation fractions, increased viscosity, and poorer spray quality. This leads to incomplete combustion in the cylinder, black smoke, and reduced engine efficiency. Therefore, selecting an appropriate cetane range is critical. Generally, for high-speed diesel engines, the cetane number should be between 40–60, while for low-speed diesel engines, it should be between 30–50.

The low-temperature fluidity of diesel is a key factor affecting the winter operation of diesel generator sets. At low temperatures, paraffin and water in diesel begin to crystallize, making the diesel cloudy; this temperature is called the cloud point. As the temperature drops further, paraffin crystals form a network structure, making the diesel lose fluidity; this temperature is called the pour point. Normally, the cloud point is 5–10°C higher than the pour point.

Domestic light diesel is graded according to the pour point. For example, No.-10 light diesel has a pour point of -10°C. If the pour point is too high, in winter the oil circuit and filter may easily clog, causing insufficient or interrupted fuel supply. Therefore, when selecting diesel, its pour point should be 4–6°C lower than the lowest ambient temperature to ensure normal operation of the generator set in cold environments.

The atomization performance of diesel directly affects its combustion effect in the cylinder. Viscosity is an important parameter for measuring the physical properties of fuel, determining the spray quality and combustion efficiency of diesel. The higher the viscosity, the larger the fuel droplets in the spray, resulting in poor combustion; if viscosity is too low, leakage and wear of the injection pump and nozzles increase.

Generally, the kinematic viscosity of light diesel at 20°C should be between 2.5–8 mm²/s. Appropriate viscosity ensures that diesel forms a good combustible mixture in the cylinder, improves combustion efficiency, and reduces pollutant emissions.

The distillation range is an indicator for measuring the volatility of diesel, reflecting the evaporation of diesel at different temperatures. The lighter the fractions, the faster the evaporation, which helps form the combustible mixture. However, if fractions are too light, too much mixture is formed during the ignition delay, and pressure rises sharply after ignition, causing rough operation. Conversely, if fractions are too heavy, evaporation is too slow, and in high-speed diesel engines combustion may begin before evaporation is complete, producing black smoke.

Therefore, choosing an appropriate distillation range is essential to ensure the efficient operation of diesel generator sets. Generally, the distillation range of light diesel should be moderate to guarantee good combustion performance under different conditions.

The cleanliness of diesel is an important factor affecting the performance and lifespan of diesel generator sets. Impurities and water severely affect the normal operation of the fuel system. Particle contamination causes wear to injectors and fuel pumps, reducing reliability. Water displaces lubricating components in fuel, lowering diesel's lubricity and damaging nozzles. In addition, water can freeze at low temperatures, blocking the fuel system, especially when wax forms around ice crystals.

To ensure diesel cleanliness, choose clean diesel that meets national standards, and regularly check the tank and fuel system to prevent impurities and water from entering. During transportation and storage, maintain the tank's cleanliness and sealing to avoid contamination.

Fuel stability is a key factor for the long-term operation of diesel generator sets. Unstable fuel forms insoluble gums and asphaltenes, which clog filters and injectors, affecting combustion efficiency and causing power loss. Inferior fuel may also become acidic, corroding engine and fuel system components.

To ensure fuel stability, choose high-quality diesel and control temperature and humidity during storage. Regularly check the fuel system and replace aged fuel in time to effectively prevent degradation and system damage.

Ensuring the efficient operation of diesel generator sets depends on using high-quality fuel. However, since fuel quality varies in the market, knowing how to accurately judge diesel quality is a skill users must master. Below are some practical testing methods to help users easily identify diesel quality and ensure stable operation of generator sets.

Qualified No.0 light diesel is usually light yellow or yellow, sometimes with a greenish hue, and clear and transparent. If diesel appears cloudy, black, or colorless, it is likely unqualified. In addition, qualified No.0 light diesel has an oily or pungent smell; if it has a foul odor, it is usually unqualified.

At room temperature, the specific gravity of No.0 light diesel is about 0.85. If density is too high, the diesel dry point is too high, combustion is incomplete, and black smoke and carbon deposits are likely; if density is too low, there are too many low-carbon components, which may cause knocking, weak acceleration, or too low flash point. Density can be tested with a densimeter or judged by observing engine operation during use.

The flash point is an indicator of the fire hazard of diesel. The national standard requires a flash point of 55°C (closed cup). If the flash point is too low, diesel is prone to fire hazards during storage and transportation. Measurement can be done with a flash point tester to ensure compliance with standards.

The grade of diesel is based on the pour point. For example, No.0 light diesel has a pour point of 0°C. In winter, if the pour point is too high, oil pipes may clog and the engine may stall. A simple test can measure the pour point: put about 200 mL of diesel into a clean, dry 300 mL plastic bottle, freeze in a refrigerator for 1–2 hours, then use a thermometer with proper range to measure its melting point, and determine if the diesel is qualified.

Ensuring the efficient operation and long service life of diesel generator sets requires not only high-quality fuel but also scientific and reasonable maintenance and management. Good maintenance practices can timely identify potential problems, prevent failures, and ensure stable operation. Below are some key suggestions for maintenance and management.

Regularly check the fuel system and replace filters and injectors in time to effectively prevent equipment damage caused by inferior fuel. Generally, the service life of injectors should reach 15,000 hours, and that of filter elements 1,000 hours or more. If these components fail prematurely, fuel quality should be examined.

Although the frequency of fuel testing is usually lower than that of lubricating oil, when reliability issues occur with diesel engines, fuel should be tested. Standard tests can detect density, distillation range, cetane index, viscosity, flash point, and acid value. Contamination tests can report water and particle content, microbial growth, and harmful metals. Fuel degradation, asphaltenes, and storage stability can also be assessed with appropriate tests. When other tests fail to indicate the causes of pump and injector failures, lubricity evaluation can be performed. Fuel testing not only provides resources for troubleshooting but also serves as a regular check of tank cleanliness and integrity, which is especially useful for standby diesel generator sets and demanding service environments.

The efficient operation and long service life of diesel generator sets rely on high-quality fuel. By understanding key indicators such as cetane number, low-temperature fluidity, atomization performance, volatility, cleanliness, and stability, users can better choose suitable fuel. Meanwhile, through simple testing methods and regular maintenance, fuel quality can be ensured, preventing equipment damage from poor fuel. Choosing clean diesel that meets national standards, regularly inspecting and replacing fuel system components, not only extends the service life of generator sets but also improves operating efficiency and reduces operating costs.